The overall objective of this project is to more clearly understand the sequence of events involved in the replication of single-stranded (SS) 0X174 DNA and the control of SS DNA replication. We have been studying an unusual mode of DNA synthesis characteristic of mutant infections defective in all gene functions for which productive SS synthesis does not occur (genes B, C, D, F, and G). This is an asymmetric non-productive synthesis in which the viral strands of the progeny RF molecules are turned over in a manner consistent with normal SS synthesis coupled to a concomitant degradation of the 5'-P tail. This nonproductive synthesis is mediated by DNA polymerase III but apparently not by DNA polymerase I. One hypothesis consistent with the data is that SS synthesis, complexing of structural and other proteins with the SS tail, and subsequent particle maturation are all intimately linked. Any perturbation which interferes with particle maturation makes the SS tail vulnerable to enzymatic degradation. We plan to experimentally test the predictions that can be made from this hypothesis. Other experiments are planned to further characterize the nonproductive synthesis as well as normal particle maturation.